An EMPA researcher holds a thin film solar cell.  (Source: EMPA)

CIGS efficiency has trended upwards over the last decade and are expected to continue to rise towards the levels of traditional silicon panels.  (Source: EMPA)

Flexible film cells could be worked into ski jackets and other wearables to provide power for electronics on the go.  (Source: Google Images)
Swiss researchers reach a record 18.7 efficiency with a flexible film cell design

Imagine having pants that charged your phone automatically, a ski jacket that charged your MP3 player, or a backpack that charged your laptop.  All of these scenarios sound great, but they all require a power source.

Solar power is one of the most promising solutions for charging low-power electronics on the go, but current cell designs are either inflexible (making them not conducive for wearable applications) or have low efficiencies.  So that perfect solar vest of your dreams hasn't become reality quite yet.

But a team of researchers at the Swiss Federal Laboratories for Materials Science and Technology (EMPA) have, at last, announced [PDF] a new record-efficient flexible film cell that almost matches silicon cell efficiency, opening the door to a wealth of commercial opportunities.

I. Record Efficiency Reached

The scientific community's dedication to solar power has yielded a lot of valuable progress over the past several decades.  This progress has tended to be iterative rather than revolutionary.

Silicon photovoltaic panels slowly crept up to efficiencies where they became financially feasible for power generation.  Now flexible film cells are making a similar climb.

The goal of the EMPA team was two-fold -- first to improve the base efficiency of flexible films and secondly to improve their manufacturability.

Pairing with FLISOM, a start-up company who is scaling up and commercializing the technology, the EMPA team were able to milk out 14.1 percent efficiency by 2005.

The EMPA team's designs focused on Copper indium gallium (di)selenide (CIGS) cells.  The CIGS metal film tended to be a promising material for flexible cells.  While the element indium remains expensive, none of the ingredients are exceedingly rare -- an issue for more novel chemistries.

Since 2005 researchers elsewhere have achieved efficiencies of up to 17.5 using a CIGS film deposited on a steel film substrate.  However these cells required expensive, hard to manufacture diffusion barriers.  They also required a 550°C growth temperature.

II. Cool Runnings -- New Cells Offer Several Improvements

The EMPA team has been hard at work coming up with a simpler design.

Their most recent work shows efficiencies of 18.7 percent being reached without a diffusion barrier.  Better yet, the awesome results were obtained from a film grown at a far lower temperature than past designs.  States research lead Ayodhya N. Tiwari, "Our results clearly show the advantages of the low-temperature CIGS deposition process for achieving highest efficiency flexible solar cells on polymer as well as metal foils."

The results could be game changing as they show a thin film that's almost as efficient as the ~20 percent efficiency of the average traditional silicon panels.  

States Professor Tiwari, "The new record value for flexible CIGS solar cells of 18.7% nearly closes the "efficiency gap" to solar cells based on polycrystalline silicon (Si) wafers or CIGS thin film cells on glass. [F]lexible and lightweight CIGS solar cells with efficiencies comparable to the "best-in-class" will have excellent potential to bring about a paradigm shift and to enable low-cost solar electricity in the near future."

While some applications like wearable electronics are obviously of high interest, the highly efficient thin-film cells could even be eyed as a replacement for traditional cells in solar windows,solar-shingles, or ground-based solar installations.  

A thin film could drastically reduce maintenance costs by reducing the weather and sediment related wear by replacing the relatively fail glass-like silicon with hardy plastics or metal films.

III. What's Next?

The EMPA team is looking to continue to bump efficiencies even higher.  But at this point they're also working to commercialize the tech via FLISOM.  The team is currently working to scale up the low temperature deposition process for mass production.

The work is funded by the Swiss National Science Foundation (SNSF), the Commission for Technology and Innovation (CTI), the Swiss Federal Office of Energy (SFOE), EU Framework Programmes, and two private firms -- W. Blösch AG and FLISOM.

Much of the details on the process remain unpublished and proprietary, unlike traditional university research, in which more information is shared.  Nonetheless, EMPA was quick to release a press release boasting of the record 18.7 percent efficiency, much as a university research team would.

As the technology becomes more established, more details about the precise process improvements should be shared.

"The Space Elevator will be built about 50 years after everyone stops laughing" -- Sir Arthur C. Clarke

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